Printing machines of this type, like such equipment as magnetic drum memories or magnetic disk units, are used for recording data and include a magnetic recording substrate that takes various forms, such as a drum, an endless belt or a disk, and is covered with a film of magnetic material. Recording data on this substrate is effected by a recording device known as a transducer, which includes one or more magnetic recording heads in the vicinity of which this recording substrate is displaced. Each time each of these heads is excited by an electric current of suitable intensity, it generates a magnetic field which has the effect of creating magnetized domains of small dimensions on the surface of the recording substrate moving past these heads. These domains, which are virtually punctiform, are generally known as magnetized points. The portion of the substrate surface that accordingly passes before each head is conventionally known as the data recording track, and the recording substrate generally includes a plurality of tracks that can be recorded upon either individually in the course of successive recording operations, or simultaneously in the course of a single operation.
To obtain better definition of the magnetized domains or points formed on the recording substrate, it has been proposed that this substrate be magnetized by what is known as "transversal" recording, such that the magnetic induction of each of the domains thus formed is perpendicular to the surface of this substrate. One such mode of magnetization proves to be of particular interest in the case of magnetic printing machines, where to obtain a printed image having high definition, it is necessary to record on the carrier a latent magnetic image that comprises various points that are quite small and quite close together. To record this latent magnetic image, the prior art has made use of a transducer including a plurality of magnetized heads arranged side by side and aligned in a direction that is perpendicular to the direction of displacement of the recording substrate. Each of these heads includes a thin magnetic core on which an excitation winding is wound, which is substantially in the shape of a "U" and is profiled so that it has a relatively narrow recording pole at one end and a relatively large flux closing pole at its other end, the two poles being put in contact with or in immediate proximity to the surface of the recording substrate.
With these heads, perfectly defined magnetized points that are relatively small in size can be obtained on the recording substrate, that is, having a square section on the surface of the substrate that is on the order of 100 to 200 .mu.m on a side. However, they have the disadvantage that each one includes a core, which must be machined with very high precision during manufacture, if the magnetized points formed by these various heads are to be substantially identical in size. Furthermore, with these heads the time required for forming one magnetized point on the recording substrate is always relatively long, in generally more than six microseconds, which naturally limits the performance of the machine in which these heads are used.
These disadvantages can be overcome by having recourse to recording heads having a magnetic core, provided with an excitation winding, which is in the form of a rod or needle, excitation winding, which is in the form of a rod or needle, each of the cores of these heads having one end disposed at least in immediate proximity to the surface of the recording substrate, these ends being aligned in succession with one another in a direction perpendicular to the direction of displacement of the recording substrate. With these heads, the core of which is easy to manufacture, the time required for recording one magnetized point does not exceed two microseconds. Nevertheless, it has always been difficult to place these heads all on the inside of the same transducer, particularly because the cores are so small in diameter and have such poor rigidity.
This is why, in an embodiment described and shown in French Patent No. 2.228.253, corresponding to U.S. Pat. No. 3,890,623 in which the fliamentary cores have a diameter on the order of 0.8 millimeters, this placement of the heads is obtained by first piercing a first series of aligned holes in a first support plate, each hole having a diameter sufficient to engage one of the two ends of a core with a slight amount of play, then inserting each core, provided with its coil, in each of these holes to keep them in place on this first support plate; then piercing a second series of holes in a second support plate such that this second series of holes are located perpendicularly to the holes of the first series, and finally causing the other end of each core to engage the corresponding hole of this second series.
This mode of assembly, which may be used where the magnetic cores are at least 0.5 millimeters in diameter, cannot be used if the magnetic transducer to be produced has heads with magnetic cores of very small diameter, for instance less than 0.1 millimeters. As a result, filamentary magnetic cores, having a very slight diameter, would not have sufficient mechanical rigidity to withstand the various assembly operations described above without becoming deformed thereby.